A review of the available world literature revealed a total of 90 cases of thyroidal hemiagenesis. An additional 4 cases are reported, 3 of which also had absence of the isthmus. All 4 patients had the left lobe of the thyroid absent. As in previously reported cases, absence of the left lobe was more common. In this study, the left lobe was absent in 80% of the cases and the right lobe was absent in 20% of the cases (a left to right hemiagenesis ratio of 4:1). The isthmus was absent in 50% of the patients where the isthmus was specifically mentioned. Females accounted for 75% and males accounted for 25% of the cases, giving a female to male ratio of 3:1. Associated disease in the remaining thyroid lobe included adenocarcinoma, hyperthyroidism, primary and secondary hypothyroidism, benign adenoma, multinodular goiter, hyperparathyroidism, and chronic thyroiditis. Some patients were found to be in a euthyroid state without abnormalities. The most common disease of the remaining lobe was hyperthyroidism. Thyroidal hemiagenesis with an isthmus present has the appearance of a hockey stick.

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